1. Field of the Invention
The present invention relates to an electric control apparatus for auger type ice making machines, and more particularly to an electric control apparatus for protecting the ice making machine from an excessive load applied thereto in operation.
2. Discussion of the Prior Art
As schematically illustrated in FIG. 3, a conventional auger type ice making machine incorporates an auger which is mounted for rotary movement within the cylindrical housing 4 of an evaporator 41 to which water is supplied to cause ice crystals to form on the internal freezing surface of the evaporator housing. As the auger is driven by an electric motor 2, the helical blade thereof scrapes the ice crystals off the internal freezing surface of the evaporator housing 4 and advances the scraped ice crystals upwardly toward an extruding head 6. The ice compressed at the extruding head 6 is broken by a breaker blade and delivered as pieces of hard ice to an ice storage bin 8. The storage bin 8 has an opening arranged to permit the pieces of hard ice to move outwardly along an appropriate chute. If in operation the delivery chute is blocked up due to the pieces of hard ice accumulated thereon, the storage bin 8 will be fully filled with the pieces of hard ice delivered from the extruding head 6. As a result, the pieces of hard ice are frozen in the storage bin 8 to cause an excessive load acting on the auger. To eliminate such an excessive load acting on the auger, a pressure gauge 42 is provided to detect a pressure drop of refrigerant in the refrigeration circuit, and a hot gas valve 43 is disposed in a bypass line of the refrigeration circuit to be opened for dissolution of the frozen ice when the pressure drop of refrigerant has been detected by the pressure guage 42.
In Japanese Utility Model Publication No. 61-28999, there has been proposed an electric control apparatus for the auger type- ice making machine which includes a movable plate arranged to be pushed up by the pieces of hard ice packed in the storage bin and a normally open detection switch associated with the movable plate to deactivate the electric motor for the ice making machine when it has been closed by upward movement of the movable-plate. In operation of the ice making machine, the ice crystals in the evaporator housing are frozen during a shortage or during suspension of the water supply to the auger. Such an abnormal freezing phenomenon of ice crystals may not be avoided by the control apparatus described above. To avoid the abnormal freezing phenomenon caused by the shortage of the water supply, Japanese Patent Publication No. 57-41669 discloses an electric control apparatus for an auger type ice making machine which includes a water level detector arranged to detect the level of water in the evaporator housing thereby to deactivate the electric motor for the ice making machine when an abnormal fall of the water level is detected. To avoid the abnormal freezing phenomenon caused by suspension of the water supply, Japanese Utility Model Publication No. 60-17655 discloses an electric control apparatus for an auger type ice making machine which includes a float switch disposed in a water tank in communication with the evaporator housing to detect the level of water in the water tank thereby to deactivate the electric motor and compressor for the ice making machine when an abnormal fall of the water level is detected.
Under control of the hot gas valve described above, the pressure drop of the refrigerant in the refrigeration circuit is detected after the ice crystals in the evaporator housing have been frozen. It is, therefore, impossible to avoid the occurrence of an excessive load acting on the auger and the abnormal freezing phenomenon caused by a shortage of the water supply. When a constant pressure expansion valve is adapted to maintain the pressure of the refrigerant in the refrigeration circuit at a predetermined level, the control of the hot gas valve may not be adapted. It is further apparent that the detection switch associated with the movable plate is useless to avoid the abnormal freezing phenomenon in the evaporator housing caused by suspension of water supply, whereas the water level detector is useless to eliminate an excessive load caused by the pieces of hard ice packed in the storage bin.